This is one of those distinctions I have to think through when writing. The use of oral doesn't seem to trouble anyone—that means words you speak. The problem comes with verbal, because it's not limited to spoken words. The words can be written or spoken.
"I have a verbal agreement," Mac said.
"Was it written or oral?" Tina asked.
Tina's question is correct. Verbal refers to the use of words, not to the form of communication. Verbal communication can be written or spoken.
If I refer to words spoken aloud, I use oral;
If I refer to the use of words, written or oral, I use verbal.